low impact development (lid) construction and …...technical information on the design,...

Low Impact Development (LID) Construction and

Maintenance Guidance Manual Written in conjunction with the RiverSmart DVD

Version 1.0, May 2009

Low Impact Development (LID) Construction and Maintenance Guidance Manual, Version 1.0, May 2009

District Department of the Environment (DDOE)

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Prepared for:

District of Columbia

Department of the Environment

51 N Street NE

Washington, D.C. 20002

Prepared by:

Low Impact Development Center, Inc.

4600 Powder Mill Road, Suite 200

Beltsville, MD 20705



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Table of Contents

1.0 Introduction ....................................................................................................................... 5

2.0 Purpose............................................................................................................................... 5

3.0 LID Practice 1: Infiltration Devices (Infiltration Trenches/Dry Wells) ...................... 6

3.1 Infiltration Device Description ....................................................................................... 6

3.2 Infiltration Device Location ............................................................................................ 6

3.3 Infiltration Device Design and Construction .................................................................. 7

3.4 Infiltration Device Maintenance ..................................................................................... 7

3.5 Infiltration Device Inspection ......................................................................................... 8

4.0 LID Practice 2: Permeable Pavement ............................................................................. 9

4.1 Permeable Pavement Description ................................................................................... 9

4.2 Permeable Pavement Design and Construction ............................................................ 10

4.3 Permeable Pavement Maintenance ............................................................................... 11

5.0 LID Practice 3: Rain Garden/Bioretention .................................................................. 13

5.1 Rain Garden/Bioretention Description ......................................................................... 13

5.2 Rain Garden/Bioretention Location .............................................................................. 13

5.3 Rain Garden/Bioretention Design and Construction .................................................... 14

5.3.1 Design: Sizing Bioretention for Water Quality Volume (Vw) Requirements ....... 14

5.3.2 Design: Volume .................................................................................................... 15

5.3.3 Construction .......................................................................................................... 15

5.4 Rain Garden Inspection................................................................................................. 16

5.5 Rain Garden/Bioretention Maintenance ....................................................................... 17

6.0 LID Practice 4: Rain Barrel/Rainwater Harvesting .................................................... 18

6.1 Rain Barrel/Rainwater Harvesting Description ............................................................ 18

6.2 Rain Barrel/Rainwater Harvesting Location ................................................................. 18

6.3 Rain Barrel/Rainwater Harvesting Design and Construction ....................................... 18

6.4 Rain Barrel/Rainwater Harvesting Maintenance .......................................................... 20

7.0 Appendix A: Permitting Requirements ........................................................................ 21

7.1 Stormwater Regulations in the District ......................................................................... 21

7.2 Submitting a Project Plan and Permit Acquisition ....................................................... 21

7.2.1 Why Do I Need a Plan and Permit? ...................................................................... 21

7.2.2 Where Can I Obtain General Information Involving the Submission of Project

Plans and Permit Acquisition? .............................................................................................. 21

7.2.3 Where Should I Submit My Application and Plan? .............................................. 22

7.2.4 How Do I Request a Pre-Development Meeting? ................................................. 22

7.2.5 What are the Plan Review and Approval Procedures? ......................................... 22

7.2.6 How Do I Obtain Information on Flood Zones? ................................................... 22

7.2.7 How Do I Obtain Information on Soil Characteristics? ........................................ 22

7.2.8 Flow Chart of Permit Plan Process ....................................................................... 23

8.0 Appendix B: General Inspection Requirements .......................................................... 24

8.1 Why Would I Need an Inspection? ............................................................................... 24

8.2 Types of Inspections the Branch Performs ................................................................... 24

8.2.1 Soil Erosion and Sedimentation Control Inspection ............................................. 24

8.2.2 Stormwater Management Construction Inspection ............................................... 24

8.2.3 Stormwater Management Facility Inspection for Preventive Maintenance .......... 24



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8.3 How Do I Schedule an Inspection? ............................................................................... 24

8.4 Infiltration Device Construction Inspection Report ...................................................... 25

8.5 Stormwater Infiltration Facility Dewatering Log ......................................................... 26

8.6 Infiltration Device Maintenance Inspection Report ...................................................... 27

8.7 Bioretention Construction Inspection Report (Page 1) ................................................. 28

8.8 Bioretention Construction Inspection Report (Page 2) ................................................. 29

8.9 Bioretention Maintenance Inspection Report ............................................................... 30

9.0 Additional Resources ...................................................................................................... 31

10.0 Acknowledgements ......................................................................................................... 32



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1.0 Introduction

This Low Impact Development (LID) Construction and Maintenance Guidance Manual was

funded by the District of Columbia, District Department of the Environment (DDOE)/Watershed

Protection Division (WPD). The Federal government,

District government agencies, and developers, the Federal

government, and District government agencies are all

interested in Low Impact Development (LID). They are

responding to the potential cost savings, superior

environmental protection, and other community development

and environmental improvements that they are seeing from

the initial LID pilot projects in the District. These groups

need to be better informed about the potential uses and

benefits so they can begin an open dialogue and form

strategies on how to incorporate LID into their development

and operations programs. Many organizations and groups see

LID as only an environmental control for stormwater, but

LID can provide numerous other economic and community

development features. For example, building occupants in high-density areas are long-term users

and can take advantage of many of the energy and water conservation measures that LID offers.

2.0 Purpose

The purpose of this guidance manual is to accompany the RiverSmart DVD and provide

technical information on the design, construction, inspection, and maintenance of four (4) LID

practices:

1. Infiltration Devices

2. Permeable Pavers/Pavement

3. Rain Gardens/Bioretention

4. Rain Barrels/Rainwater Harvesting

The objectives of this effort are to provide outreach materials for several targeted audiences to

increase awareness about LID and to facilitate dialogue between permit agencies, engineers,

developers, students, and DDOE staff.

Target Audiences

Developers and community development corporations

Property management companies and community associations

District of Columbia public and private school students

Staff persons from the District Department of the Environment (DDOE)

Federal and District agencies involved in construction projects

Appendix A includes information on the District of Columbia stormwater regulations and

permitting process, while Appendix B provides an overview of the DDOE inspection process.

This will include information on how LID can be used to comply with the Department of

Consumer and Regulatory Affairs (DCRA) and DDOE regulations and permit process.

What is LID?

LID is a stormwater management

strategy concerned with maintaining

or restoring the natural hydrologic

functions of a site to achieve natural

resource protection objectives. LID

addresses stormwater through small,

cost-effective site design and

landscape features that are

distributed throughout the site. LID

projects/programs promote public

awareness, education, and

participation in environmental

protection.



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3.0 LID Practice 1: Infiltration Devices (Infiltration Trenches/Dry Wells)

3.1 Infiltration Device Description

Infiltration is one example of an LID technique that retains and treats stormwater on-site. This

reduces the excessive, unnatural, and destructive volume of stormwater runoff that damages the

quality of our waterways. Infiltration also reduces

the amount of stormwater piped to the Blue Plains

Advanced Wastewater Treatment Plant (AWTP).

The Blue Plains AWTP receives wastewater

collected from the Maryland and Virginia suburbs

and by the District of Columbia sewer system.

Stormwater infiltration increases the amount of

rainwater that is absorbed into the soil and helps

recharge groundwater aquifers1. Rainwater from a

roof or paved surface may be piped directly into

an infiltration device. The rainwater may also flow

directly across pavement into stormwater inlets or be carried via a grassed swale to an infiltration

device. Infiltration trenches and dry wells are examples of infiltration devices typically used

when there are suitable conditions in urban areas.

Infiltration devices are trenches or basins that have been backfilled2 with stone. These infiltration

basins, trenches, or dry wells collect runoff during a storm event and release it into the soil by

infiltration. This process protects nearby streams by reducing total stormwater runoff volume,

filtering pollutants, recharging groundwater, and preserving baseflow. Stormwater that is treated

by infiltration trenches is first stored in the spaces between stone aggregate3 called “voids.” The

number and size of the voids is dependent on the

size and type of aggregate being used.

3.2 Infiltration Device Location

Infiltration devices must be located more than 10

feet from a building foundation, on reasonably

level ground with no steep slopes. They may not

be installed where any toxic spill has occurred or

where on-going soil remediation is being

performed. Infiltration trenches may be used in

conjunction with another stormwater management

device, such as a detention pond, to provide additional water quality control and peak flow

attenuation. Runoff that contains high levels of sediments or hydrocarbons (oil and grease) that

may clog the trench must be pretreated with other devices such as grit chambers, water quality

inlets, sediment traps, swales, or grass filter strips.

1 Aquifer: An underground bed or layer of earth, gravel, or porous stone that is saturated and sufficiently permeable

to yield water to wells or springs. Typically used or could be used as a source of water, for drinking or other

purposes. 2 Backfill: The act of refilling an excavation location or material used to refill the excavation location or hole.

3 Stone Aggregate: Crushed stone bound together.

Source: RiverSmart DVD




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3.3 Infiltration Device Design and Construction

The size of the infiltration device is the first design consideration. Specific calculations are used

to determine the anticipated amount of

stormwater that will run off the pavement, roof, or

lawn and into the infiltration device during a rain

event. In the District of Columbia, an infiltration

device must treat the first ½ inch of rain from a

storm4. For example, a paved area 50 feet X 100

feet long is anticipated to produce 208 cubic feet

of stormwater runoff after ½ inch of rain has

fallen.

The design engineer then proposes a size for the

infiltration device that will accommodate the

required volume of stone, while meeting other building code restrictions. A vertical pipe or

observation well allows the owner, maintenance worker, or District inspector to see if the trench

is functioning correctly. By looking into the observation well you can see standing water or dry

stone aggregate. Standing water 72 hours after a rain event indicates that the infiltration device

has a draw down time, or is dewatering5 too

slowly and may need repair or replacement. Dry

stone 72 hours after a rain event indicates that the

infiltration device is working as designed for

stormwater treatment.

A sand layer is typically at the bottom of the

infiltration devices. This layer separates the stone

aggregate from the subsoil. The sand provides a

final filtering of the water before it is absorbed

into the subsoil and becomes groundwater.

Filter cloth is used to separate the stone from the

on-site soils. The filter cloth should be woven

monofilament and comply with the District Stormwater Guidebook standards and specifications.

Infiltration trench effectiveness and life cycle is extended when pretreatment such as vegetated

filter strips or grassed swales is included in the design.

3.4 Infiltration Device Maintenance

The principal maintenance objective is to prevent clogging, which may lead to failure of the

infiltration device. If standing water is present three (3) days after a rain event, it indicates that

the infiltration trench is draining too slowly and needs maintenance. Preventative maintenance

4 This is the current District of Columbia water quality standard as of March 2009. The proposed new water quality

treatment standard will require capturing and treating the runoff volume from one (1) inch of rainfall to meet water

quality requirements, and a further enhanced stormwater quality and quantity control standard for the Anacostia

Waterfront Redevelopment Zone. 5 Dewatering: Removal or drainage of water.





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(e.g. maintaining the pretreatment BMPs) will lengthen the life of the infiltration trench. Reseed

any eroded areas in the grass filter strip immediately, and isolate those areas until they have

recovered. The grass height should always be equal to or greater than the design flow depth.

Remove accumulated debris annually from the pretreatment devices and stormwater inlets.

3.5 Infiltration Device Inspection

Periodic inspections of the construction of the infiltration device must be made by the DDOE

Stormwater Inspector.

1. The DDOE Stormwater Inspector will

study the materials used, construction

quality, and the dimensions of all

components of the device.

2. The goal of the inspection is to insure that

every infiltration device within the District

is both safe and functional and constructed

to the specifications of the approved

Stormwater Plan. Once the permit is

signed, but prior to final hook-up and use of

the Infiltration Device, a DDOE Stormwater Inspector must conduct a final inspection of

the completed Infiltration Device. Then the contractor can back fill the device, and

remove the water-tight seals on the inflow pipes.

3. As with all permitted stormwater devices in the District, a final inspection of the

completed device must be scheduled with the DDOE and an As-Built plan must be

submitted for review and approval by the DDOE within 21 days of the final inspection

date.




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4.0 LID Practice 2: Permeable Pavement

4.1 Permeable Pavement Description

Permeable pavement consists of open-graded asphalt or

concrete that allows for the infiltration of stormwater into

the sub soils or stone aggregate for storage rather than

creating runoff. Conventional pavement causes rainwater to

run off, creating excessive costs for municipal stormwater

systems and excessive water quality problems, flooding,

and damage to the streams and aquatic life. Permeable

pavement controls runoff volume and peak discharge6,

filters pollutants, and may be used to recharge groundwater

by allowing rainwater to pass through the pavement and

flow through voids between the aggregate and into the

ground.

There are five (5) standard types of permeable pavement, including certain types that can bear

the weight of a vehicle.

1. Free-Standing Permeable Pavers are the

least stable of the five types and are

therefore only recommended for light and

infrequent load-bearing, such as private

walkways or infrequently-used portions of

driveways. This being the most basic type

of permeable pavers, it uses free-standing

bricks, concrete blocks or flat stones laid

on a bed of sand and stone aggregate.

2. Permeable Interlocking Concrete Pavement (PICP) is a more sophisticated form of

permeable paver that is designed for:

Parking lots

Driveways

Patios

Private walkways and public

sidewalks

Low traffic roads

Parking lanes

Nature trails & park pathways

Environmentally sensitive

developments

PICP is comprised of a layer of durable concrete pavers separated by joints filled with

small stones. The blocks are impervious, but the joints allow infiltration. The joints, or

6 The rapid flow of water is infiltrated, meaning that large storms bypass after some infiltration thus decreasing the

peak discharge.






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interlocking shapes, vary considerably from simple notches to built-in concrete joint

spacers.

3. Concrete Grid Pavement (CGP) is an extensive concrete grid that uses large spaces filled

with stone aggregate or with sod and turf.

The reinforced concrete structure provides

stability for bearing the weight of vehicles

and the stone or sod-filled spaces provide

permeability. There are two types of CGP:

i) Poured-in-Place Concrete Slabs

ii) Pre-Cast Concrete Grids.

4. Pervious Concrete (PC) looks like

conventional concrete when installed. The

difference is that it will allow rainwater to flow

through it to the bedding and base layers for infiltration into the ground. Pervious

Concrete is Portland cement7 with the use of sand or fines.

5. Pervious Asphalt (PA) is a permeable asphalt pavement, also known as porous asphalt, is

similar to pervious concrete. It is standard hot-mix asphalt with reduced sand or fines and

allows water to drain through it into a

crushed stone reservoir.

4.2 Permeable Pavement Design and

Construction

Permeable pavers may be used for parking lots,

driveways, road shoulders, and pedestrian paths.

Such paving should not be used in areas with

the potential for spills, such as gas stations or

loading docks. Construction of permeable

pavers is similar to that of conventional

pavements. Installation of paver blocks will

require additional time for placement of the

blocks. Similar materials and construction

techniques are required for permeable and

conventional pavements. The largest difference

is the depth of the aggregate subbase, which is used for additional storage volume of stormwater

and the addition of geotextile material.

With all five (5) types of permeable pavement, there are basic installation considerations:

7 Portland Cement: The most common type of cement used. It is a hydraulic cement made by heating a limestone

and clay mixture in a kiln and pulverizing the resulting material. Typically used with water and sand or gravel to

make concrete or mortar.

Installation of permeable, or porous asphalt in the parking lanes and conventional asphalt in the drive lanes in Portland, OR.

Source: Portland Bureau of Environmental Services (BES)




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1. As with most pavement, never install

during rain or over frozen base material.

2. Permeable pavement works best on level

ground.

3. Landscape the site so that no stormwater

drains to the pavers from the surrounding

landscape. Such drainage may carry silt,

which would clog the drainage spaces

between the pavers or the permeable

surface.

4. Minimize all opportunities for the spillage

of toxic liquids onto the permeable pavement.

Such toxins would infiltrate into the soil and groundwater.

5. Permeable pavers work best if the base of the structure is at least 3 feet above the high

water table8 level of the soil. If the high water table is closer than 3 feet, an underdrain

pipe may need to be installed in the base layer to drain excess water to another

stormwater device. The purpose of the underdrain is to prevent standing water on the

paved surface when the soil becomes super-

saturated.

6. While installation costs may be higher in

some instances for permeable pavers than for

conventional pavement, these cost increases

can be offset by the decreased costs of

stormwater management.

7. In the case of the RiverSmart Home Program,

the District government may be able to assist

you financially if you install permeable

pavers. For more information on this program,

go to ddoe.dc.gov/riversmarthomes or call

(202) 535-2240.

4.3 Permeable Pavement Maintenance

The primary purpose of cleaning and maintaining your permeable

paver system is to make sure that the drainage voids, or openings,

in the surface are clean and clear from all kinds of debris and

maintain efficiency. Debris will clog up the drainage voids of your

pavement and in turn reduce the flow capacity of the system. If

you installed grass pavers you should treat them as you would your

lawn, by regularly watering, mowing, and weeding.

8 Water Table: Generally referring to the water level, or upper surface of the groundwater. Level fluctuates

seasonally and year to year as climatic conditions change.


Source: DDOE

Source: DDOE

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Interlocking concrete pavers and porous concrete require more care. These surfaces need to be

kept clean and free of debris, so it is necessary to

vacuum and wash these types of permeable paver

systems, so as to keep the voids clear and to allow

them to function as they should for treatment of

stormwater. You can use street sweepers and

vacuums to maintain these types of pavers, and

should carry out the procedure about four (4)

times a year. It is also a good idea to check the

level of the fill material in the voids of

interlocking pavers, and re-fill them when

necessary, particularly after pressure cleaning.

Five (5) general maintenance considerations:

1. You should inspect your site on a regular basis; after the installation. You should inspect

it once a month for about four (4) to six (6) months. After this time period you can

inspect the site annually, or after a particularly heavy rain event when the drainage voids

can become clogged with debris.

2. Every three (3) months you should get into the habit of sweeping and vacuuming your

permeable surface. You can use street sweepers that have a vacuum and brushes, which

help clean out the voids in your paver

system, restoring permeability.

3. It is also a good idea to apply high pressure

hosing to the site after you have swept and

vacuumed it thoroughly. Check that the

voids are still well-filled with aggregate. It

may be necessary to refill them regularly,

using clean stone or gravel.

4. Settlement9 of paver block systems may

require resetting. Cracks and settlement in

asphalt or concrete may require cutting and

replacing the pavement section.

5. The application of abrasive materials for snow treatment should be prohibited in order to

prevent clogging.

9 Settlement: Occurs when individual pavers or groups of pavers near curbs, site fixtures, walls, or at locations

where pavers meet other surfacing materials.

Source: Interlocking Concrete Pavement Institute (ICPI)



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5.0 LID Practice 3: Rain Garden/Bioretention

5.1 Rain Garden/Bioretention Description

A simple, yet effective method to control stormwater is through the use of rain gardens, also

known as bioretention cells. Rain gardens are

small vegetated depressions that collect, store,

and in some cases, infiltrate stormwater runoff.

They contain a special soil mix, or media,

typically consisting of 50 percent sand, 30

percent organic material, and 20 percent topsoil

(by volume). It uses very little of the onsite soils

and tends to be sandy. The size and depth of a

rain garden, or bioretention cell, varies

depending on the drainage area and location of

the storm sewer. Beyond its use for stormwater

control, the rain garden provides aesthetically

pleasing landscaping and a natural habitat for

birds and butterflies. Finally, rain gardens promote

sustainable design practices while encouraging environmental stewardship and community pride.

5.2 Rain Garden/Bioretention Location

Rain gardens/biorentention cells proposed for

compliance with the District of Columbia storm

water regulations as part of the Building Permit

process must have a Geotechnical Report10

prepared by an engineer registered with the District.

The report must document that the proposed

location for bioretention has soils that will infiltrate

one (1) inch of water or better within 24 hours.

Rain gardens/bioretention cells are generally sited

uphill of existing stormwater inlets for retrofit

projects and allow stormwater to enter via curb cuts

or grass swales for parking lots and residential areas.

For new construction, they are typically located at the lowest elevation on the site closest to the

storm sewer.

Finding a good location for a rain garden involves balancing a number of different factors:

10 Geotechnical Report: Prepared by a geotechnical engineer or geologist. It provides details on the effects of

drainage and drainage facilities on soil characteristics, geology and groundwater.

Source: DDOE

Source: DDOE



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A rain garden should be located in a place where it will receive runoff. Check to make

sure runoff flows to your site, or could flow with minor modifications, such as cutting a

space out of a curb.

Rain gardens are typically located at least ten (10) feet from the building to avoid damage

to the foundation depending on the geotechnical report for permitted rain gardens. A ten

(10) foot separation from the building is a good rule of thumb for homeowner retrofit rain

garden projects.

Find out where underground utilities are buried. Common utilities may include water,

sewer, electrical, gas, telephone and cable lines, as well as sprinkler systems. Before

construction, you can contact Miss Utility, which will locate utilities for free. Please visit

the Miss Utility website for more information. www.missutility.net/

5.3 Rain Garden/Bioretention Design and Construction

5.3.1 Design: Sizing Bioretention for Water Quality Volume (Vw) Requirements

A simplified bioretention sizing method for water quality

treatment in the District may use the following criteria. First

the Water Quality Volume (Vw) is calculated:

Where:

Vw = (R x Ia)

12

Vw = Water quality volume to be treated (cubic feet)

R = Runoff depth, use 0.5 (for treatment of one half

inch of rain)

Ia = Impervious area to be treated = length x width (square feet)

12 = Conversion factor (for conversion of feet to inches)

Example: An impervious area 60 ft long x 12 ft wide (60’x 12’) equals 720 square feet (sf) of

imperviousness.

Vw = (0.5 ft x 720 sf)

12

Vw = 30 cubic feet of stormwater to be treated

Note regarding ½” of runoff: This is the current District of Columbia

water quality standard as of March 2009. The proposed new water quality

treatment standard will require capturing and treating the runoff volume

from one (1) inch of rainfall to meet water quality requirements. In

addition, a further enhanced stormwater quality and water quantity

standard will be required for the Anacostia Waterfront Development

Zone.


http://www.missutility.net/



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5.3.2 Design: Volume

The available storage for a proposed bioretention/rain garden size is then computed. For our

example a 4’x 10’ rain garden is proposed. The total amount of area available for storage is a

combination of the surface ponding area plus the storage area available from the void space

within the media.

(Proposed surface ponding area) + (Proposed available surface area x Media depth x Void space)

Where:

Surface ponding area = 4’ x 10’ = 40 square feet (sf)

(40 sf x 1’ ponding area) + (40 sf x 2’ media x 0.35 void space) = 42 cubic feet available

for storage and treatment of the anticipated runoff for a one half inch storm.

Bioretention/rain gardens are generally 5 to 7 percent of the total drainage area, and should be

able to store 75 percent of the stormwater runoff before it infiltrates or bypasses the remaining 25

percent of stormwater. More detailed information for sizing Low Impact Development

stormwater best management practices can be found in the District Department of the

Environment Stormwater Guide Book.

5.3.3 Construction

Typical Bioretention Cross-section

Source: U.S. Environmental Protection Agency



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Construction includes soil excavation (digging), construction of plumbing components, surface

grading, soil replacement, and planting native plants. Because rain gardens/bioretention cells are

sensitive to sediment loading, the surrounding area needs to be completely stabilized before the

rain garden is put into place.

The rain garden site should be well protected with silt

fence11

or other erosion and sediment control best

management practices. These precautions are needed to

ensure that construction debris and sediment do not foul

the rain garden bed. A rock weir12

that serves as an

energy dissipater for inflow of stormwater at the curb

opening or inlets should be at least two (2) times the

width and at least three (3) times the length as the

required curb opening in order to prevent erosion of the

rain garden bed from the inflow of stormwater. Large rip-rap

stone 6” in depth minimum on a liner of filter fabric is required.

After construction is complete and all plumbing components have been connected and final back

filling and grading of the rain garden bed has occurred, a shredded hard wood mulch cover,

uniform in color and free of foreign materials, is required to cover the entire rain garden bed to a

depth of 2-3 inches.

5.4 Rain Garden Inspection

1. For permitted rain garden construction, the contractor shall arrange a “preconstruction

meeting” with the permit applicant or their agent and the DDOE stormwater inspector

prior to beginning work on the rain garden/bioretention facility.

2. Inspections shall be performed:

a. At the completion of excavation to inspect the sub grade preparation;

b. During underdrain and plumbing components construction and connection, and

for the soil or media or installation;

c. During backfilling. “Soil Certification” for backfill is required.

3. The final top soil shall be thoroughly wetted to achieve the design top soil elevation.

4. Additional back fill should be placed to reach the design elevations.

5. The final grading shall be inspected by the DDOE stormwater inspector before planting.

6. Sediment and erosion control measures may be removed upon approval by the DDOE

stormwater inspector.

11 Silt Fence: Temporary barrier made of woven, synthetic filtration fabric supported by steel or wood posts. It

prevents sediment carried by sheet flow from leaving the construction site. 12

Weir: A structure, or barrier, placed across an opening or conduit to interrupt flow.

Source: DDOE



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What alternatives are available for capturing rainwater from storms greater than ½ inch?

1. Overflow Drain

2. Underdrain

3. No Plan – Not recommended

5.5 Rain Garden/Bioretention Maintenance

Immediately after the completion of construction, water plant material for 14 consecutive days

unless there is sufficient natural rainfall. After

storm events, inspect the area and make sure that

drainage paths are clear and that ponding water

dissipates over 24 hours. The inlet is a particular

focus for maintenance. If inlets are not clear and

cleaned out regularly, they clog up and the water

by-passes.

Routine maintenance should include a visual

inspection for removal of accumulated sediment,

trash, and debris; repair of erosion; repair to stone

weirs; visual inspection of the rain garden bed and

inlets; and visual inspection of the condition of

the perennials, shrubs, and tress. Add a fresh mulch

layer every year and remove any mulch that has become fouled with oil and grease or other

hazardous.



Pre-maintenance

Embedded stone weir and over grown with weeds.

Source: DDOE

Post-maintenance

Removal of weeds and repair of stone weirs at inlets.

Source: DDOE



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6.0 LID Practice 4: Rain Barrel/Rainwater Harvesting

6.1 Rain Barrel/Rainwater Harvesting Description

A rainwater harvesting/collection system is a tank modified with a filter, plus an inflow, outflow,

and overflow piping network that captures

stormwater runoff from the downspouts of

buildings. The system safely stores this

chlorine-free water for later use during dry

weather. Most residential systems use

tanks that are installed above-ground,

which is cost-effective and allows for

energy-free, gravity-based release of

harvested stormwater.

Rain barrels are low-cost water conservation devices that can be used to reduce runoff volume

and, for smaller storm events, delay and reduce the peak runoff flow rates (i.e. maximum

instantaneous flow rate during a storm event). By

storing and diverting runoff from impervious

areas such as roofs, these devices reduce the

undesirable impacts of runoff that would

otherwise flow swiftly into receiving waters and

contribute to flooding and erosion problems.

6.2 Rain Barrel/Rainwater Harvesting

Location

Rain barrels are placed outside of a building at roof

downspouts to store rooftop runoff for later use in lawn and garden watering.

6.3 Rain Barrel/Rainwater Harvesting Design and Construction

Rain barrel sizing is relatively simple. Rain barrels store between 55 and 100 gallons and may

be connected in series for additional capacity. Space constraints and frequency and volume of

water used will determine the number of rain barrels needed. Rain barrels can be purchased from

a supplier or, for a lower cost option, you

can make your own.

Homemade rain barrels are relatively easy

to construct. Basic components consist of

the following:

1. One or more 55-gallon barrels

2. A child-resistant top, or screen, that

allows easy access for cleaning.

Screens may be used at the inflow

points to strain coarse sediment and

reduce the potential for mosquito

breeding.






- 19 -

3. Connections to the downspout, overflow pipe, and spigot, and hoses to connect barrels in

series (if applicable).

Installing a rainwater collection system involves the use of a simple formula to determine how

much water can be collected from a downspout.

1. First, decide which downspout will be used to collect the rooftop stormwater runoff.

2. Next, determine what portion of the floor space of the house is under the portion of the

roof that drains into that downspout.

3. Estimate or measure, in feet, the length and the width of the roof area that drains to the

downspout that will be connected to the rain barrel or cistern. Then, multiply the length

by the width to determine the square footage. For example, if the length is 20 feet and

the width is 15 feet, then the product is 300 square feet.

4. During an average rain event, a reasonable estimate of the amount of rain that will drain

through a downspout is about two-thirds of a gallon of rainwater per square foot. For

example, a rough estimate of rooftop

runoff in a one-inch rainstorm can then

be represented as two-thirds of a gallon

of stormwater runoff multiplied by the

square footage of the floor space under

the roof.

5. In our example, the estimated runoff

would be two-thirds of a gallon per

square foot times 300 square feet. The

product would then be 200 gallons of

water that could be collected in a tank for every

one-inch of rainfall. Since the average rain per event in the District is a one-half inch

rainfall, the average rainfall would deliver 100 gallons into the tank for this home.

6. A homeowner can have a successful system with any size tank. It is important to

consider that the smaller the tank, the more important it is to have a large overflow

system that can deliver the overflow volume to a place that will not create flooding

anywhere. The larger the tank, the less

concern is needed for overflow and the

more water will be available for

irrigation during dry days.

7. Tanks can range from 50 gallons to

20,000 gallons of storage capacity.

8. Filters can be purchased or built and

range from simple leaf collectors to

highly efficient commercial filters. A filter

should be installed that keeps mosquitoes out of

the tank. All filters must be placed between the downspout outfall and the entry point

into the tank.

9. The inflow, outflow, and overflow holes in the tank are generally drilled by the tank

manufacturer or installer. A homeowner installing a tank can use a 3-4” hole saw to

drill the inflow holes and a smaller hole saw for a hose fitting for the out flow.





- 20 -

10. The inflow area must be at the top of the tank and be the same size or larger than the

downspout.

11. The overflow needs to be at least the same size as the downspout, but preferably larger.

A larger overflow allows for the tank to overflow more efficiently. Polyethylene or

ABS pipe is recommended for the overflow pipe. The overflow pipe can be drained into

another RiverSmart feature, such as a rain garden, or directed to the municipal

stormwater system. Be sure it drains much more than 10 feet from the foundation of

any structure and never drains onto neighboring property.

12. The outflow or spigot for release of the water must be as close to the bottom of the tank

as possible. The seal on the spigot needs to be water-tight and checked regularly, as the

water pressure on the spigot can be significant.

13. Connect a standard garden hose for irrigation and you are ready to begin watering your

garden with your own supply of chlorine-free rain water. While at the same time you

have helped to reduce some of the impacts associated with stormwater runoff from your

roof.

6.4 Rain Barrel/Rainwater Harvesting Maintenance

Maintenance requirements for rain barrels are minimal and consist only of regular inspection by

the homeowner of the unit as a whole and any of

its constituent parts and accessories. The unit and

attachments should be inspected for clogging

several times a year and after major storms.

Minor parts such as spigots, screens, downspouts,

and connections may need to be replaced.

NOTE: Make sure to empty the rain barrel between rainstorms and during winter prior to a

freeze.




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7.0 Appendix A: Permitting Requirements

7.1 Stormwater Regulations in the District

District of Columbia Stormwater Management Regulations, §509 through §518 of D.C.

Municipal Regulations, Title 21, Chapter 5, of the D.C. Water Pollution Control Act of 1984,

authorizes the District to ensure that best management practices (BMPs) are used to control

stormwater runoff from new development and redevelopment projects. Additionally, all land

disturbing activities are regulated under D.C. soil erosion and sedimentation control regulations

outlined in D.C. Municipal Regulations, Title 21, Chapter 5. The primary function of DDOE’s

Compliance and Enforcement Program is to enforce these laws and associated regulations.

7.2 Submitting a Project Plan and Permit Acquisition

7.2.1 Why Do I Need a Plan and Permit?

Land disturbing activities are regulated under law. As such, no person may engage in any land

disturbing activity on any property within the District until

that person has secured a construction permit from the

District. Approval of a Construction Permit (dcra.dc.gov) is

based upon the simultaneous submission by the permit

applicant of an Erosion and Sediment Control Plan, a

Stormwater Management Plan, or both, depending on the

nature of the development activity. An erosion and sediment

control plan is required for 50 square feet or greater of land

disturbance. A Stormwater Management Plan is required for

5000 square feet of land disturbance. The regulations

governing stormwater management, erosion and sediment

control, and floodplain management are outlined in Chapter

5 of Title 21, District of Columbia Municipal Regulations (DCMR). Copies of the DCMR can be

purchased at the Office of Documents and Administrative Issuances (ODAI), Room 520, 441 4th

Street, NW, Washington, D.C. 20001. os.dc.gov

7.2.2 Where Can I Obtain General Information Involving the Submission of

Project Plans and Permit Acquisition?

The Department of Consumer and Regulatory Affairs (DCRA) has established a “Permit Service

Center” on the second floor at 941 North Capitol Street, NE, Washington, D.C., to assist

businesses, developers, and other permit applicants seeking general information regarding

permits, application materials, and technical assistance. The center is open for business from

8:30 a.m. to 4:45 p.m., Monday through Friday. The Department of the Environment has staff

persons stationed at the “Permit Service Center” to provide assistance to customers to ensure that

permit applications, construction plans, and environmental forms and documents that are

submitted to acquire a permit, meet regulatory requirements. For inquiries, you may call any of

the phone numbers listed below: (202) 442-4696 or (202) 442-4686 or (202) 442-9518 or go to

dcra.dc.gov/.

Note: All SWM BMPs must also be recorded at the Recorder of Deeds in the Office of Tax and

Revenue. Go to otr.cfo.dc.gov for more information.

Exceptions for Homeowners An Erosion and Sediment Control

Plan is not required when earth

disturbing activities are limited to

individual spread footings to

support columns, fence post holes,

and utility service connection and

repairs. Participants in the

RiverSmart Homes program must

have a home audit to determine

exemption from stormwater

permits.

http://dcra.dc.gov/

http://os.dc.gov/

http://dcra.dc.gov/

http://otr.cfo.dc.gov/



- 22 -

7.2.3 Where Should I Submit My Application and Plan?

All plans along with permit applications and other related documents (if required) must be

submitted to the “Permit Service Center” at 941 North Capitol Street, NE, 2nd floor, for

screening. Projects that qualify for immediate approval will be handled at the “Permit Service

Center” by the Department of the Environment staff located at the center. All other projects (file

jobs) will be forwarded to the Technical Services Branch - Watershed Protection Division (51 N

Street, NE, 5th Floor, Washington D.C. 20002) for review.

7.2.4 How Do I Request a Pre-Development Meeting?

A preliminary meeting between the developer/designee(s)/applicant and the technical review

staff of the Technical Services Branch is recommended during the conceptual phase of project

design to discuss design strategy or issues related to best management practices for stormwater

management and sediment control. To request and schedule a meeting, please call the Watershed

Protection Division’s main line: (202) 535-2240.

7.2.5 What are the Plan Review and Approval Procedures?

Within 10 to 30 working days of the submission of a plan, the technical review staff of the

Sediment and Stormwater Technical Services Branch shall review the plan and make a

determination to approve or disapprove the plan. If it is determined that more information is

needed or that a significant number of changes must be made before the plan can be approved,

the applicant will be informed in writing to make the necessary changes and resubmit the revised

plan. All re-submissions must contain a list of the changes made. A new 10 to 30 day review

period begins on the date of the re-submission. If plan approval is denied, the reason(s) for the

action shall be communicated to the applicant in writing.

7.2.6 How Do I Obtain Information on Flood Zones?

If you need to know whether a specific property is located in a flood zone as defined by the

Federal Emergency Management Agency (FEMA), you can call the Watershed Protection

Division for assistance at (202) 535-2240.

7.2.7 How Do I Obtain Information on Soil Characteristics?

If you need to know whether a specific property is located in problem soils in the “Urban land-

Christiana-Sunnyside association13

” as identified by the District of Columbia Soil Survey

Manual, which was produced for the District by the US Department of Agriculture (USDA)

Natural Resources Conservation Service (NRCS), you can call the Watershed Protection

Division for assistance at (202) 535-2240, or go to the D.C. GIS website (dcgis.dc.gov/)

13 Urban land-Christiana-Sunnyside association: The most prevalent general soil association in the District portion

of the watershed. These predominantly upland soils are deep, nearly level to steep, well-drained soils that are

underlain by unstable clayey sediment.

http://dcgis.dc.gov/



- 23 -

7.2.8 Flow Chart of Permit Plan Process



- 24 -

8.0 Appendix B: General Inspection Requirements

8.1 Why Would I Need an Inspection?

Land disturbing activities of greater than 50 square feet are regulated under law. The Inspection

and Enforcement Branch of DDOE performs the functions listed below as part of its mandate to

implement the inspection and enforcement component of the soil erosion and sedimentation

control and stormwater management regulations. These regulations are outlined in Chapter 5 of

Title 21, District of Columbia Municipal Regulations.

8.2 Types of Inspections the Branch Performs

8.2.1 Soil Erosion and Sedimentation Control Inspection

Inspectors are authorized to conduct periodic inspections of all land disturbing activity at

construction sites to ensure compliance with approved plans and to determine if the measures in

the approved plans are providing effective control. Inspectors also conduct final inspections

within four (4) weeks after receiving notice of project completion to ensure compliance with

final site stabilization as specified in the approved plan.

8.2.2 Stormwater Management Construction Inspection

Inspectors are authorized to conduct on-site inspections of all stormwater management facilities

constructed in the District of Columbia. A pre-construction meeting is the first step in a

stormwater management facility inspection. At this meeting an inspection schedule and

requirements are discussed. Inspections are then performed at different stages of construction as

specified in the sequence of construction to ensure compliance with the approved plans.

The owner/contractor is responsible for notifying the Inspection and Enforcement Branch at least

24 hours before construction for a pre-construction meeting and within one (1) week after

completion of the permitted facility for final inspection. The registered professional engineer

with responsibility to certify the As-Built plan is required to submit the As-Built plan for the

stormwater management facility to the Branch within twenty-one (21) days after final inspection.

8.2.3 Stormwater Management Facility Inspection for Preventive Maintenance

Inspections are performed after servicing of all stormwater management facilities in operation in

the District of Columbia. If maintenance is required after initial inspection of the facility, a letter

of notification is sent to the property owner or person designated as being responsible for

maintenance (usually the property owner). Inspectors also ensure that the maintenance schedule

and agreements are recorded with the Recorder of Deeds in the Office of Tax and Revenue as a

specific Declaration of Covenant.

8.3 How Do I Schedule an Inspection?

All land disturbing activities require a building permit. After obtaining a building permit from

the D.C. Department of Consumer and Regulatory Affairs, the owner/contractor is required to

call the Inspection and Enforcement Branch at least 24 hours before the start of excavation or

grading to schedule a pre-construction meeting or an initial site inspection. Please call (202) 535-2977 for inspection scheduling.



- 25 -

8.4 Infiltration Device Construction Inspection Report



- 26 -

8.5 Stormwater Infiltration Facility Dewatering Log

Inspection

Date

Rain

Date

Dewatering

Date

Maintenance

Service Date



- 27 -

8.6 Infiltration Device Maintenance Inspection Report



- 28 -

8.7 Bioretention Construction Inspection Report (Page 1)



- 29 -

8.8 Bioretention Construction Inspection Report (Page 2)



- 30 -

8.9 Bioretention Maintenance Inspection Report



- 31 -

9.0 Additional Resources

District of Columbia Department of the Environment (DDOE). May 2001. Stormwater

Management Guidebook.

Schueler, T. 1995. Site Planning for Urban Stream Protection. Metropolitan Washington

Council of Governments. Washington, D.C.

Natural Resources Defense Council (NRDC). May 1999. Stormwater Strategies: Community

Responses to Runoff Pollution. www.nrdc.org/water/pollution/storm/stoinx.asp

National Resources Defense Council (NRDC). July 2002. Out of the Gutter: Reducing Polluted

Runoff in the District of Columbia. www.nrdc.org/water/pollution/gutter/gutterinx.asp

LID Techniques

General

www.lid-stormwater.net/site_map.htm

www.epa.gov/owm/mtb/mtbfact.htm

www.duluthstreams.org/stormwater/toolkit/tools.html

Infiltration Devices

www.epa.gov/npdes/pubs/infltrenc.pdf

Miss Utility

www.missutility.net/

Permeable Pavement

www.lid-stormwater.net/permpavers_benefits.htm

www.epa.gov/owow/nps/pavements.pdf

www.icpi.org/

www.nrmca.org/

Rain Garden/Bioretention

www.raingardens.org/Index.php

www.mninter.net/~stack/rain/

www.lowimpactdevelopment.org/raingarden_design/

Rain Barrels

www.mapc.org/regional_planning/LID/cisterns_barrels.html

www.stormwatercenter.net/Pollution_Prevention_Factsheets/rain_barrels.htm

www.lid-stormwater.net/raincist_home.htm

Research

www.udc.edu/dc_water_resources/about_us.htm (University of the District of Columbia)

www.ence.umd.edu/~apdavis/Bioongoing.htm (University of Maryland)

http://www.nrdc.org/water/pollution/storm/stoinx.asp

http://www.nrdc.org/water/pollution/gutter/gutterinx.asp

http://www.lid-stormwater.net/site_map.htm

http://www.epa.gov/owm/mtb/mtbfact.htm

http://www.duluthstreams.org/stormwater/toolkit/tools.html

http://www.epa.gov/npdes/pubs/infltrenc.pdf

http://www.missutility.net/

http://www.lid-stormwater.net/permpavers_benefits.htm

http://www.epa.gov/owow/nps/pavements.pdf

http://www.icpi.org/

http://www.nrmca.org/

http://www.raingardens.org/Index.php

http://www.mninter.net/~stack/rain/

http://www.lowimpactdevelopment.org/raingarden_design/

http://www.mapc.org/regional_planning/LID/cisterns_barrels.html

http://www.stormwatercenter.net/Pollution_Prevention_Factsheets/rain_barrels.htm

http://www.lid-stormwater.net/raincist_home.htm

http://www.udc.edu/dc_water_resources/about_us.htm

http://www.ence.umd.edu/~apdavis/Bioongoing.htm



- 32 -

10.0 Acknowledgements

David Eckert Producer, Virginia Village Productions

Michael Hamilton Videographer, Hamilton Video

Sheila Besse Associate Director, Watershed Protection Division, District Department of

the Environment

Walter Caldwell Environmental Protection Specialist, District Department of the

Environment

Joanne Goodwin Grants Coordinator, Fisheries and Wildlife Division, District Department

of the Environment

George Hawkins Director, District Department of the Environment

Dr. Hamid Karimi Deputy Director, District Department of the Environment

Bryan King Associate Director, Fisheries and Wildlife Division District Department of

the Environment

Timothy Karikari Branch Chief, Sediment Storm Water and Technical Review Branch

District Department of the Environment

Abdi Musse Acting Chief of Inspection and Enforcement, District Department of the

Environment

Tari Caldwell Development Researcher, The Nature Conservancy

Ann English Landscape Architect, Low Impact Development Center, Inc.

Megan Kirby Office Assistant, Low Impact Development Center, Inc.

Robb Lukes Environmental Engineer, Low Impact Development Center, Inc.

Michelle Pawlish Environmental Scientist, Low Impact Development Center, Inc.

Neil Weinstein Executive Director, Low Impact Development Center, Inc.